Utilization of the broadcast spectrum is changing and moving away from a monolithic model in which single types of content, such as television broadcast signals, were broadcast in the spectrum to a multicasting model in which multiple types of content and services are broadcast simultaneously. In order to achieve such diverse utilization of the broadcast spectrum, data must be multiplexed into a signal and mapped to specific physical resources within the transmitted signal.
FIG. 1 illustrates an overview of the process 100 for generating an Orthogonal Frequency Division Multiplexed (OFDM) transmitted signal at the physical layer. Data in the form of information bits belonging to one or more Physical Layer Pipes PLP1 through PLPn (hereinafter referred to as “PLP”) 102 arrives. It should be appreciated that each PLP 102 carries data associated with a particular service. For example, a PLP 102 may carry data associated with a television program, the video stream for a program, the audio stream for a program, closed-caption information, or data associated with other suitable types of services.
The data belonging to each PLP 102 is sent through Forward Error Correction (“FEC”) 103 coding, such as Low Density Parity Check (“LDPC”) coding or turbo coding. The coded bits are used to modulate 104 a constellation symbol using a modulation approach such as Quadrature Phase Shift Keying (“QPSK”), for example. Time interleaving 106 may optionally be applied to the modulation symbols.
The resulting modulation symbols from one or multiple PLPs 102 are then mapped 108 to specific resources or data cells within a block of resources. Such a block of resources may be termed as a frame, as a partition within a frame, or as a sub-frame within a frame. Specifically, a partition can be thought of as a subset of resources within a frame, with a frame containing one or more partitions. The block of resources can be represented as a logical grid 200 of data cells with dimensions in both time and frequency domains, as illustrated in FIG. 2. For example, each data cell 202 can carry one modulation symbol while each column 204 of data cells belongs to one OFDM symbol.
Referring back to FIG. 1, the data cells belonging to each OFDM symbol may undergo optional frequency interleaving 110 on a per OFDM symbol basis in order to improve frequency diversity. Scattered pilot, edge pilot, and/or continual pilot values are inserted 112 at appropriate locations within each OFDM symbol to assist with channel estimation and carrier tracking at a receiver. The resulting multiplexed data and pilot cells then undergo an Inverse Fast Fourier Transform (“IFFT”) 114 on a per OFDM symbol basis. Peak to Average Power Ratio (“PAPR”) reduction techniques 116 may optionally be applied to the resulting signal. Finally, a Guard Interval (“GI”) or cyclic prefix is prepended 118 to the time-domain samples for each OFDM symbol.
It should be appreciated that are three types of OFDM symbols. At the beginning of each frame or partition, zero or more OFDM symbols carrying preamble signaling may be present. Preamble signaling contains information about how PLPs are encoded, modulated, and mapped to resources within the transmitted signaling. These are followed by one or more data OFDM symbols. An optional frame or partition closing symbol may be present as the final OFDM symbol of a frame or partition.
Each of the three types of OFDM symbols, if present, may carry one or more data cells if space is available. The number of data cells per OFDM symbol is constant within a particular type of OFDM symbol. Conversely, the number of data cells per OFDM symbol may be different when comparing two different types of OFDM symbol.
A linear one-dimensional logical addressing scheme, such as the addressing scheme 300 used in the DVB-T2 standard and illustrated in FIG. 3, has been commonly used to facilitate the mapping 108 or addressing of PLPs to specific data cells within blocks described. As illustrated, NSP represents the number of OFDM symbols carrying preamble signaling and available to carry payload data (NSP≥0), NSD represents the number of OFDM symbols carrying normal data (NSD≥1), NSC represents the number of frame closing symbols that are present (0≤NSC≤1), NCP represents the number of data cells carried in preamble OFDM symbols if such OFDM symbols are present and available to carry payload data, NCD represents the number of data cells carried per normal data OFDM symbol, and NCC represents the number of data cells carried in the frame closing symbol if a frame closing symbol is present. Logical indexing of the data cells begins with the first available data cell of the first OFDM symbol belonging to the frame or partition, and then continues on with the remaining data cells of the same OFDM symbol. After all of the data cells belonging to an OFDM symbol have been indexed, indexing moves to the first data cell of the next OFDM symbol. It should be appreciated that the frame or partition closing symbol, if present, generally contains fewer data cells than a normal data OFDM symbol due to the frame closing symbol carrying more pilots.
It should be appreciated that in DVB-T2, PLPs are classified as either Type-1 or Type-2 PLPs. Data cells belonging to a Type-1 PLP are all contiguous in terms of logical data cell addresses. In particular, all Type-1 PLPs contained in a particular frame or partition are mapped to data cells starting at the beginning of the frame or partition. All of the Type-1 PLPs are mapped to contiguous blocks of data cells before any of the Type-2 PLPs are mapped to data cells. That is, the logical addresses of all of the data cells belonging to all of the Type-1 PLPs present in a frame or partition have a lower logical address value than any of the data cells belonging to any of the Type-2 PLPs present in the same frame or partition.
The data cells belonging to a Type-2 PLP, on the other hand, are not all contiguous in terms of logical data cell addresses. Rather, a technique called sub-slicing is used to divide each Type-2 PLP into a set of equal-sized sub-slices, where each sub-slice consists of a set of contiguously-addressed data cells. For example, a Type-2 PLP with a total size of 1000 data cells might be divided into ten (10) sub-slices, with each sub-slice consisting of 100 contiguously-addressed data cells. However, the logical address locations of the ten (10) sub-slices would not represent ten (10) contiguous blocks of addresses but the ten (10) blocks would instead be distributed throughout the frame or partition.
In DVB-T2, sub-slices from multiple Type-2 PLPs are interleaved with each other. That is, the first sub-slice of the first Type-2 PLP will appear, the first sub-slice of the second Type-2 PLP will then appear, and so on with all of the first sub-slices of all of the Type-2 PLPs present in a frame or partition. Following this collection of first sub-slices, the second sub-slice of the first Type-2 PLP will appear, the second sub-slice of the second Type-2 PLP will appear, and so on. This continues until all rounds of sub-slices have been completed.
In DVB-T2, a super-frame is defined as a group of multiple contiguous in-time frames. The values of certain control signaling fields are constrained to remain fixed over the duration of a super-frame.
In order to facilitate resource mapping, the DVB-T2 standard includes control signaling in a preamble which is located at the beginning of each frame. Relevant portions of this preamble include the L1-Post signaling, which carries the bulk of the control signaling describing the contents of each frame and of the overall super-frame. The L1-Post is itself divided into several parts, including a configurable portion and a dynamic portion. Control signaling contained in the configurable part of the L1-Post is constrained to remain static or fixed over the duration of a super-frame while control signaling contained in the dynamic part of the L1-Post may vary from one frame to another within the same super-frame.
It should be appreciated, however, that although the DVB-T2 standard may be adequate for use in example systems that only send a single type of service or data such as TV broadcasting program, since there is no need to change parameters often, the DVB-T2 standard is not flexible. Rather, the standard is restrictive in terms of options available for mapping to data cells and ability to change parameters often. In particular, the DVB-T2 standard imposes the following constraints: (1) a given PLP is constrained to only be a Type-1 or Type-2 PIP but the PLP cannot switch between the two types, which limits diversity (2) all Type-1 PLPs must occur before any Type-2 PLP within the same frame; (3) Type-2 PLPs are limited in size to between 2 and 6480 sub-slices per frame; (4) the same number of sub-slices per frame must be used for all frames within a super-frame; (5) the same sub-slice interval, which indicates the number of data cells from the start of one sub-slice of a Type-2 PLP to the start of the next sub-slice of the same PLP within the current frame, must be used for all Type-2 PLPs present within the same frame; (6) all Type-2 PLPs within a given frame must have the same number of sub-slices; and (7) all Type-2 PLPs must have their first sub-slice occur before the second sub-slice of any Type-2 PLP occurs.
Thus, the DVB-T2 standard may be overly restrictive and therefore inadequate if implemented by a system, such as an ATSC 3.0 broadcast system, wherein PLPs associated with a variety of types of services may be intended to be multiplexed and broadcast via a single frame.